I've got POP on, never really have KA falses. I've had two instances where a legit cop car was Jed out, but in both cases I had the thing alerting for a long time before it did, and the joccurred right as I passed the cop... so it is an annoyance, but It did not harm detection.
I agree it is a problem, but it is more of an annoyance than a major issue... at least how its presented to me, because each time I could see that it was a legit alert before it got Jed out. And thats the crux of it. I suspect something in the cops radar gun makes the J happen... but only happen at very close range.